The membranes of chloroplast mitochondria and bacteria contain a proton ATPase which utilizes the electrochemical potential of protons for the synthesis of ATP from ADP and Pi. Similar to enzymes of other energy-transducting membranes, the chloroplast H+ ATPase consists of an intrinsic membrane sector CFO which mediates proton translocation and an extrinsic catalytic section CF1. From the known chemistry of GTP and ATP hydrolysis in other systems, it might be expected that catalysis in F type ATPase proceeds through a pentacovalent phosphate intermediate. A penta-covalent phosphorous is also assumed to be a transition state intermediate since it is readily inhibited by the Pi analog vanadate. X-ray Absorption Fine Structure (XAFS) data on vanadium edge were collected on vanadate-CF1 complex. Direct XAFS analysis of the pre-edge transitions and the EXAFS region clearly show a pentacovalent structure at the active site. These results suggests that a pentacovalent phosphorous exists as a transition state during ATP hydrolysis in CF1-ATPase from chloroplast.